This invention relates generally to a process which is employed in manufacturing semiconductor chips. More particularly, the invention relates to a process for improving the structural properties and reliability of certain materials that are utilized as integrated circuit (IC) dielectrics.
New materials with low dielectric constants (known in the art as xe2x80x9clow-k dielectricsxe2x80x9d) are being investigated for their potential use as insulators in semiconductor chip designs. A low dielectric constant material aids in enabling further reductions in the integrated circuit feature dimensions. In conventional IC processing, SiO2 is used as a basis for the dielectric material resulting in a dielectric constant of about 3.9. Moreover, advanced dense low-k dielectric materials have dielectric constants below about 2.8. The substance with the lowest dielectric constant is air (k=1.0). Therefore, porous dielectrics are very promising candidates since they have the potential to provide very low dielectric constants. Unfortunately, however, advanced low-k dielectrics typically have the problem of insufficient mechanical strength and deposition temperatures of these materials can exceed allowable thermal budgets.
Thin film dielectric coatings on electric devices are known in the art. For instance, U.S. Pat. Nos. 4,749,631 and 4,756,977, to Haluska et al., disclose silica based coatings produced by applying solutions of silicon alkoxides or hydrogen silsesquioxane, respectively, to substrates and then heating the coated substrates to a temperature between 200 and 1000xc2x0 C. The dielectric constant of these coatings is often too high for certain electronic devices and circuits.
U.S. Pat. Nos. 4,847,162 and 4,842,888, to Haluska et al., teach the formation of nitrided silica coatings by heating hydrogen silsesquioxane resin and silicate esters, respectively, to a temperature between 200 and 1000xc2x0 C. in the presence of ammonia.
Glasser et al., Journal of Non-Crystalline Solids, 64 (1984) pp. 209-221, teaches the formation of ceramic coatings by heating tetraethoxysilane in the presence of ammonia. This reference teaches the use of anhydrous ammonia and that the resulting silica coatings are nitrided.
U.S. Pat. No. 4,636,440, to Jada, discloses a method of reducing the drying time for a sol-gel coated substrate comprising exposing the substrate to aqueous quaternary ammonium hydroxide and/or alkanol amine compounds. Jada requires that the coating be dried prior to heating. It is specifically limited to hydrolyzed or partially hydrolyzed silicon alkoxides.
U.S. Pat. No. 5,262,201, to Chandra et al., and U.S. Pat. No. 5,116,637, to Baney et al., teach the use of basic catalysts to lower the temperature necessary for the conversion of various preceramic materials, all involving hydrogen silsesquioxane, to ceramic coatings. These references teach the removal of solvent before the coating is exposed to the basic catalysts.
U.S. Pat. No. 5,547,703, to Camilletti et al., teaches a method for forming low dielectric constant Sixe2x80x94O containing coatings on substrates comprising heating a hydrogen silsesquioxane resin successively under wet ammonia, dry ammonia, and oxygen. The resultant coatings have dielectric constants as low as 2.42 at 1 MHz. This reference teaches the removal of solvent before converting the coating to a ceramic.
U.S. Pat. No. 5,523,163, to Balance et al., teaches a method for forming Sixe2x80x94O containing coatings on substrates comprising heating a hydrogen silsesquioxane resin to convert it to a Sixe2x80x94O containing ceramic coating and then exposing the coating to an annealing atmosphere containing hydrogen gas. The resultant coatings have dielectric constants as low as 2.773. The reference teaches the removal of solvent before converting the coating to a ceramic.
U.S. Pat. No. 5,618,878, to Syktich et al., discloses coating compositions containing hydrogen silsesquioxane resin dissolved in saturated alkyl hydrocarbons useful for forming thick ceramic coatings. The alkyl hydrocarbons disclosed are those up to dodecane. The reference does not teach exposure of the coated substrates to basic catalysts before solvent removal.
U.S. Pat. No. 6,231,989, to Chung et al., entitled xe2x80x9cMETHOD OF FORMING COATINGSxe2x80x9d, discloses a method of making porous network coatings with low dielectric constants. The method comprises depositing a coating on a substrate with a solution comprising a resin containing at least 2 Sixe2x80x94H groups and a solvent in a manner in which at least 5 volume % of the solvent remains in the coating after deposition. The coating is then exposed to an environment comprising a basic catalyst and water. Finally, the solvent is evaporated from the coating to form a porous network. If desired, the coating can be cured by heating to form a ceramic. Films made by this process have dielectric constants in the range of 1.5 to 2.4 with an elastic modulus between about 2 and about 3 GPa.
Low-k dielectric materials produced by spin-on and chemical vapor deposition processes or by a self-assembly process typically require a curing process subsequent to the deposition. Typical process conditions for curing low-k films include nitrogen purged furnace anneals at temperatures between about 350 and about 450xc2x0 C. for 30 to 180 minutes. As was described in U.S. patent application Ser. Nos. 09/681,332 (now U.S. Pat. No. 6,558,755), 09/952,649, 09/906,276, 09/952,398, and 10/627,894, the disclosures of which are incorporated herein by reference, instead of thermally curing or plasma treating, the low-k films can be UV cured at substantially shorter times or at lower temperatures, eliminating the need for prior furnace curing and therefore reducing the total thermal budget.
Moreover, there remains a need for a process for making other low-k materials with improved structural properties, such as improved elastic modulus and material hardness, without compromising or deteriorating its electrical properties.
The present invention meets that need by providing an ultraviolet curing process for advanced low-k materials.
Although the present invention is not limited to specific advantages or functionality, it is noted that the process produces materials having a low dielectric constant and an improved elastic modulus and material hardness, or produces materials with comparable modulus and hardness and can reduce the total thermal budget as compared to a furnace cure.
In accordance with one embodiment of the present invention, a process is provided for making a UV cured material comprising providing a dielectric material having a first dielectric constant, having a first elastic modulus, and having a first material hardness. The dielectric material is cured with ultraviolet (UV) radiation to produce a UV cured dielectric material having a second dielectric constant which is comparable to the first dielectric constant, having a second elastic modulus which is greater than the first elastic modulus, and having a second material hardness which is greater than the first material hardness. By xe2x80x9ccomparable toxe2x80x9d we mean within about xc2x120% of the first dielectric constant. The increase in elastic modulus and material hardness is typically greater than or about 50%.
The UV cured dielectric material can optionally be post-UV treated to provide a post-UV treated, UV cured dielectric material having a third dielectric constant, having a third elastic modulus, and having a third material hardness. Post-UV treatment of the UV cured dielectric material reduces the dielectric constant of the material while maintaining the increase in the elastic modulus and material hardness, as compared to the elastic modulus and material hardness before the post-UV treatment. More particularly, the third elastic modulus and material hardness are greater than or within about xc2x120% of the second elastic modulus and material hardness, respectively.
The process for making a UV cured material can further comprise placing the dielectric material into a process chamber, evacuating or purging the process chamber to remove room air, supplying a process gas to the process chamber, heating the dielectric material, and exposing the dielectric material to UV radiation.
In accordance with another embodiment of the present invention, a process for making a UV cured material is provided comprising providing an uncured low-k dielectric material, and UV curing the dielectric material at a time of no greater than about 5 minutes, or at a temperature of no greater than about 450xc2x0 C. to produce a UV cured dielectric material, wherein the total thermal budget of the UV curing is reduced by greater than about 50% as compared to a furnace curing process.
Accordingly, it is an object of the present invention to produce dielectric materials having improved elastic modulus and material hardness, and a low dielectric constant.
Additionally, it is a object of this invention to produce dielectric materials wherein the process of formation and curing occurs at a reduced time or reduced temperature or both, resulting in a decreased thermal budget for the process.
These and other features and advantages of the invention will be more fully understood from the following detailed description of the invention taken together with the accompanying drawings. It is noted that the scope of the claims is defined by the recitations therein and not by the specific discussion of features and advantages set forth in the present description.